The present disclosure relates to methods of forming contact regions for semiconductor structures, and more particularly, to methods of forming p-type and n-type semiconductor material contacts on a same side of a crystalline semiconductor material.
In some applications in which hydrogenated amorphous silicon (a-Si:H) and similar semiconductor materials are used as semiconductor contacts for realizing hybrid devices on crystalline semiconductor substrates, such as inter-digitated back-contact heterojunction solar cells, or bipolar junction transistors, such semiconductor contact materials need to be patterned, followed by the deposition of the next semiconductor contact material, e.g., a-Si:H (or similar semiconductor material) layer(s). To ensure a high-quality interface with a low density of interface states, the surface of the crystalline semiconductor material needs to be sufficiently clean and also typically hydrogen terminated to prevent oxidation of the crystalline semiconductor material surface prior to the deposition of the semiconductor contact material.
Since patterning of the first semiconductor contact material typically requires lithography, the deposition of the next semiconductor contact material, e.g., a-Si:H (or similar semiconductor material) layer(s), will require cleaning of the exposed surface of the crystalline semiconductor material to remove organic photoresist residues which form due to the patterning process; however, most effective cleaning techniques such RCA or piranha damage the first semiconductor contact material, e.g., a-Si:H (or similar semiconductor material) layer(s). In addition, patterning of the next semiconductor contact material will typically etch (partially or fully) or damage the first semiconductor contact material. Therefore a hard mask may be used to protect the first semiconductor contact material; however, removing the hard mask after etching will typically etch or damage the first semiconductor contact material. Removal of the hard mask may not be needed if the hard mask is comprised of a conductive material such as a metal, however, conductive materials are typically damaged during the hydrogen termination step required prior to the deposition of the second semiconductor contact material.